Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$15.81	6.532%	$16.8427	$16.84	$16.85	$16.80
Purchase #2	$53.59	11.415%	$59.7073	$59.71	$59.70	$59.70
Purchase #3	$43.55	12.126%	$48.8309	$48.83	$48.85	$48.80
Purchase #4	$6.72	13.435%	$7.6228	$7.62	$7.60	$7.60
Purchase #5	$156.50	10.709%	$173.2596	$173.26	$173.25	$173.30
Purchase #6	$34.74	9.821%	$38.1518	$38.15	$38.15	$38.20
Purchase #7	$97.89	7.323%	$105.0585	$105.06	$105.05	$105.10
7 purchase totals =	$408.80		$449.4736	$449.47	$449.45	$449.50